Pressure Cookers

The Importance of Sterilization

Every home mushroom cultivator should own a pressure cooker. It plays an essential role in the fight against contamination. They are used to sterilize grain spawn, agar, substrate, and more. Typically materials are cooked at 15 PSI for a given amount of time, which kills off any bacterial or spores. The time will vary depending on the media you are trying to sterilize. Liquids sterilize the fastest, and hardwoods take more time.

Which Pressure Cookers to Buy

There are specific criteria a pressure cooker must possess to sterilize your cultivation materials properly. When browsing pressure cookers to purchase, keep a lookout for the following necessary factors:/p>

  • PSI Gauge: Monitoring the pressure building up inside your cooker is vital, so only buy a pressure cooker with a gauge that displays the PSI.
  • Maintain 15 PSI: To kill off bacteria and unwanted fungi, a pressure cooker must reach and hold 15 PSI. Role out any cooks that fail to meet this critical requirement.
  • Capacity: Look for a cooker with a pot large enough to hold many jars or bags. A pressure cooker that can hold over 20 quarts is the perfect size for most home cultivation projects.
  • Durability: Repeat use has the potential to reak havoc on lesser quality pressure cookers. Seek one constructed with high-quality materials that will last.

Pressure Cooker Reviews

Presto 23-quart Pressure Cooker Review

Presto's 23-quart pressure cooker is ideal for sterilizing grain spawn, substate, agar, and more. The ease of use, reliability, and cost make it perfect for novice mushroom cultivators. The large 23-quart compacity fits around seven to ten 1-quart jars. Out of the box, you'll need to install the pressure gauge; then you're ready to start cooking. Typically, I can obtain 15 PSI in around 20-25 minutes, and I have very little trouble maintaining my desired PSI. After use, you'll want to dry all parts of the pressure cooker thoroughly to avoid damage. Hard water and other factors will eventually take its toll on various components, causing failure. However, proper upkeep will maintain the longevity of the presto. Replacement parts are also very reasonably priced. To keep your pressure cooker looking shiny and chrome, try using Bar Keepers Friend.

My Presto pressure cooker has many miles on it, and it hasn't let me down yet. If beginning mushroom cultivation, this pressure cooker is one of the best cost-effective options.

  • Sufficient capacity
  • Easy to operate
  • Minimal upkeep
  • Straightforward assemble
  • Reliable
  • Cost-effective
  • Certain parts will eventually fail
  • Limited stock due to the pandemic

All American Pressure Cooker

The All American brand of pressure cookers are considered to be best in class. However, without hands-on experience, I can only speak to their reputation. The only negative thing I've heard about them is the price tag, which exceeds $300.

Other Pressure Cookers

Several other affordable models should also work, but research them thoroughly before purchasing. Remember, they need to reach 15-PSI for an extended amount of time to effectively sterilize your cultivation items.

Getting to Know Your Pressure Cooker

This overview of components is for the Presto 23-quart pressure cooker, though many other brands would contain similar aspects.

Pressure Cooker Pot

The spacious 23-quart pot accommodates multiple cultivation materials in a single cycle.

If you look closely, there are measurement notches on the inside of the pot. The one closest to the bottom indicates 3 quarts. To locate them, look at the handle with the arrow on it. The arrow will point to the notches.

It is perfectly normal for the inside of the pot to become discolored over time. You can easily remove the stains by cooking a combination of water and cream of tartar at 15 PSI.

Pressure Cooker Lid / Cover
Lid / Cover

The lids contain all the critical components of the pressure cooker. To attach it to the pot, match up the arrow on the handle and lid, and then turn the lid to create a seal.

Avoid denting or damaging the cover, especially around the rim. A misshapen lid could prevent the seal, making it impossible to maintain the required pressure.

Pressure Cooker Gauge
Pressure Gauge

The pressure gauge indicates the pounds of pressure per square inch (PSI) and is one of the only parts you'll need to assemble. Before operating your pressure cooker, ensure the dial points at '0' and doesn't contain any damage. Do not submerge the gauge in water and protect it from dropping or any other damage.

You can have the gauge checked for accuracy at various locations or by sending it to the Presto consumer service department. If damaged or inaccurate, replace the gauge before using the pressure cooker.

Replace Pressure Gauge
Pressure Cooker Sealing Ring
Sealing Ring

The sealing ring is the black rubber ring that lines the inside of the lid and seals in the pressure.

Before use, always inspect the sealing ring for tears or deterioration. Dry the seal thoroughly after use to keep in ideal condition. Typically you'll need to replace the ring every 2 to 3 years from general wear and tear.

Replace Sealing Ring
Pressure Cooker Air Vent - Locking Mechanism
Air Vent/Locking Mechanism

As pressure builds, the locking mechanism will activate by popping up and locking the lid in place. It is silver and stamped with "TOP" on it. As the cooker begins to build pressure, water and steam may release from the vent, which is normal.

In time you may need to replace the gasket on the locking mechanism if it appears cracked or nicked.

Replace Air Vent/Locking Mechanism
Pressure Cooker Overpressure Plug
Overpressure Plug

Behind the pressure gauge, you'll find a black overpressure plug. It acts as a safety mechanism and will eject if the pressure reaches an unsafe level. It is expected for the plug to appear raised as pressure accumulates.

Replaced the overpressure plug is there are any signs of wear and tear.

Replace Overpressure Plug
Pressure Cooker Vent pipe
Vent Pipe

Steam and pressure release through the vent pipe. A weight is placed on top of the vent pipe to regulate pressure. Always check to ensure the vent isn't clogged. You can hold it up to a light source and, you should be able to see through it. Never use a toothpick to clean the vent pipe as pieces could break off inside. Instead, use a pipe cleaner or something durable enough that won't become lodged in the pipe.

Pressure Cooker Weight
Weight / Pressure Regulator

Once the cooker is up to temperature, you'll place the weight on the vent pipe to build and regulate pressure.

The releasing steam can become rather loud. To reduce, try adding 17 grams to the weight. This hack is entirely optional, but three quarters will work great.

Remember to remove the weight before opening the lid. It sounds like a no brainer, but I often forget, and the weight crashes to the floor

Replace Weight
Pressure Cooker Cooking Rack
Cooking Rack

The cooking rack provides space between the scorching bottom surface of the pot and your materials. Without the rack, jars have the potential to break, and bags could melt.

To prevent jars from floating inside the cooker, place small empty jars or rings from the lids under the rack. Check for and eliminate any air bubbles trapped underneath your items or spacers.

Replace Cooking Rack

How to Use a Pressure Cooker for Sterilization

1) Inspect Your Pressure Cooker

Before operating your pressure cooker, ensure that all parts are in working order.

  • Sealing Ring: No tears or damage.
  • Vent pipe: Nothing is clogging the vent.
  • Air Vent/Locking Mechanism: Not sticking and slides with ease.
  • Overpressure Plug: Fits securely to the lid and no damage.
  • Pressure Gauge: Reads zero and no signs of damage.

2) Add Water

Fill the pot with the required amount of water. Distilled water works best to maintain your cooker's longevity, but tap water works fine if you heat it beforehand. Usually, you'll need 3-quarts, which would be up to the first notch. To eliminate hard watermarks, add a few tablespoons of white vinegar.

Sometimes your jars may float, which could cause them to break. I suggest placing either a few 4oz jars or lid rings at the bottom of the cooker and then place the cooking rack on top of them. This technique will help prevent your items from floating and allows the steam to sterilize a larger surface area. If using jars, tilt them slightly to release any trapped air bubbles beneath them.

Pressure Cooker Notches

3) Prepare and Add items

Prepare your items for the pressure cooker by placing foil over any lids with filter ports. Also, fold bags to prevent steam from entering the filter patch. This technique is to block extra moisture from entering your cultivation media.

Arrange your materials securely inside the pressure cooker. If needed, try adding empty jars to prevent things from moving around and possibly breaking.

Pressure Cooker Packed

4) Seal the Lid and Start Heating

Match up the arrow on the lid with the arrow on the handle. The lid should fit snuggly to the pot when correctly aligned.

Place your pressure cooker on the stove set to high heat. Do not add the weight yet. Eventually, steam and water droplets will sporadically spit from the vent pipe. Add the weight to the vent pipe once the steam exits at a steady flow and not sputtering. It usually takes around 10 minutes to get up to temp.

Pressure Cooker Seal Lid

5) Bring Up to Temp and Monitor Pressure

Pressure will begin building within the cooker. Monitor it closely and reduce the heat once you reach the desired PSI. I typically shoot for around 17-18 PSI. At this point, you can also set your timer.

Keep adjusting the heat until you find a setting where the desired PSI is maintained. Monitor the gauge regularly to ensure the PSI holds steady.

Pressure Cooker Gauge and Weight

6) Finish Cooking

Once the allotted time expires, turn off the heat and allow the cooker to come down in pressure. DO NOT OPEN the pressure cooker until the pressure gauge reaches '0'.


You can carefully remove agar once the PSI reaches 0. While the cooker is still hot, I suggest using oven gloves to prevent burns. Allow the agar mixture to cool to around 113-122F (45-50C). An infrared temperature gun comes in handy for determining the temperature of your agar mixture. At that point, it will be ready too pour. Be advised that the agar will begin to solidify if allowed to cool too long.

Grain / Substrate / Etc

Allow the pressure cooker to cool overnight before removing items other than agar. Adding spores or mycelium to hot grain or substrate could kill the fungi.

7) Clean and Store

Once finished, clean your pressure cooker and thoroughly dry all components. Finally, store your pressure cooker in a dry place around room temp.

Common Questions

Can a pressure cooker explode?

Most pressure cookers contain an overpressure plug that ejects if the PSI begins to reach a dangerous level. The steam released when the plug activates could cause burns. However, I always run my cooker at a safe PSI, so I haven't witnessed the plug ejecting.

Should a pressure cooker hiss?

Yes. It is perfectly normal for your pressure cooker to hiss. While maintaining a particular PSI, the weight or pressure regulator allows steam to release, causing the hissing noise.

Do you need a pressure cooker to sterilize cultivation material?

There are a few innovative but risky techniques to sterilize without a pressure cooker. I wouldn't recommend them as the risk of contamination is too high.

Can you use an Instapot for sterilization?

It depends on the capabilities of the Instapot. From what I've read, they are unable to reach and maintain the required 15-PSI.

Will plastics melt in the pressure cooker?

Be careful with most plastics, and they could melt under the heat and pressure. Mushroom bags and some harder plastics can withstand the high temperatures. The general rule is that if it is oven-safe, you should be good to go.